<!DOCTYPE html>
<html lang="zn">
<head>
    <meta charset="UTF-8">
    <title>clearfix</title>
    <style>
        .box1{
            width: 200px;
            height: 200px;
            background-color: #bfa;

        }

        .box1::before{
            content: '';
            display:table ;
        }

        .box2{
            width: 100px;
            height: 100px;
            background-color: blue;
            margin-top: 100px;
        }

        /* clearfix 这个样式可以同时解决高度塌陷和外边距重叠的问题，当你在遇到这些问题时 ，直接使用clearfix这个类即可*/
        .clearfix::before,
        .clearfix::after{
            content: '';
            display: table;
            clear: both;
        }        
    </style>
</head>
<body>
    <div class="box1 clearfix">
        <div class="box2"></div>
    </div>
</body>
</html>